.big {
  margin: 0 auto;
  width: 1240px;
  display: flex;
  flex-direction: column;
  align-items: center;
}

/* 提示框 */
.alert {
  width: 400px;
  position: fixed;
  top: 50px;
  left: 50%;
  transform: translateX(-50%);
  display: none;

}

.show {
  display: block !important;
}